This invention relates to an ink-jet printer and printing method therefor which perform printing by discharging ink as ink droplets from a discharge orifice such that the ink droplets are attached to the surface of a print medium and, more particularly, to an ink-jet printer and printing method therefor which prevent feathering and bleeding, realize good color development, and form a high quality image in accordance with the image type.
Conventionally, as ink for ink-jet printing, water ink mainly is used for the purposes of safety, prevention of bad smell and the like. A known example of the water ink is obtained by dissolving or dispersing various water dyes or pigments in water, or in water and a water-soluble organic solvent, and adding a wetting agent, dye dissolution accelerating agent, antifungal agent and the like to the solvent, in accordance with necessity. The ink-jet printing method has many advantages as follows: high-speed printing can be performed by discharging such ink as several thousands of ink droplets per second; printing can be performed with reduced noise; color printing can be easily performed; printing can be performed in high resolution; and normal paper can be used in printing. Accordingly, the ink-jet printing method has become very popular in recent years.
Further, with the lowered prices and high performance of personal computers and the standardization of the GUI (Graphical User Interface) environment, there are increasing needs for good color development, high quality, good durability, high resolution and high speed in image printing by printers. For this reason, technical ideas to keep color matter on the surface of paper as much as possible, to form sharp edges of print dots, and to reduce ink spread, that is, feathering, bleeding or the like, have been proposed, and related products have been sold. These techniques are briefly classified into a printing technique which uses a print sheet called normal paper as a print medium, and a printing technique which uses paper for ink-jet printing. The normal paper, which is used in a copier and the like, is produced with low cost, and has practically excellent characteristics. Further, in recent years, paper for copiers which controls ink spread and has a certain degree of adaptability to ink-jet printing has been introduced.
To print a really high-quality image, it is necessary to use a special paper for ink-jet printing. The special paper is obtained by coating the surface layer of the paper with various materials. By using this paper, ink absorption, color development and the like are controlled, and high-quality images and characters are represented. This is a very excellent method to provide high-quality images; however, it has various practical drawbacks as follows: the cost of the special paper is high; notes cannot be easily written by a pencil or pen on the coated special paper surface; the special paper provides an unpleasant touch; the special paper cannot be used in a copier; and the weight of the paper is heavier than normal paper.
Generally, normal paper is mainly used in view of the above drawbacks of the special paper, however, it is necessary to use specialized ink for the normal paper. Ink which quickly permeates into paper is inappropriate to print sharp character images. However, if the permeation is prevented too much, the ink remains on the paper surface in a liquid state, which might dirty a finger or the like touching the ink after printing and which causes a blur by contact with the finger or the like. Accordingly, ink for printing by using normal paper is prepared in consideration of the balance between the permeability and non-permeability such that sharp characters can be printed. When printing only characters, usually black characters are printed on a white base of the paper. In this case, the ink for black characters is prepared as above.
On the other hand, color printers have been widely used in recent years. In the case of color printing, the situation is greatly different. For example, in the case of printing characters on a uniform color base, if ink in which permeability with respect to the paper is suppressed to a certain degree as above is used, the color ink mixes with another color ink at a portion where the different colors are in contact, which causes so-called feathering or bleeding. The feathering and bleeding greatly degrade image quality. Accordingly, the trend of ink in recent years in color ink-jet printing is ink which contains a surface active agent and which permeates into the paper very quickly. In the use of this ink, if printing is performed by using a first color ink and then printing is performed by using a second color ink, the first color ink used in the first printing has already permeated into the paper at the next printing. This prevents feathering and bleeding, and prints a high-quality image on normal paper. However, in a case where black characters or color characters are printed on normal paper, the edges of the characters are not sharp because the ink permeates into the paper and at the same time the ink spreads along the paper surface. Further, as the ink permeates into the inside of the paper, printing density is lowered to a certain degree due to light scattered by the fibers of the paper surface. The scattered light produces a color image in a low-saturation. For this reason, an image printed by so-called ink-jet printing on normal paper is poor in comparison with an image printed on paper for ink-jet printing.
Then, to obtain an image with high-quality upon ink-jet printing on normal paper, a technique to heat the print medium from the rear surface side of the medium, before printing, during the printing, and after the printing has been proposed.
This technique is disclosed in, e.g., Japanese Patent Application Laid-Open No. 56-82290. Further, Japanese Patent Application Laid-Open Nos. 62-135368 and 62-173259 propose providing a plurality of heaters. However, these techniques aim to finally realize a unique temperature in the entire area of a print medium regarding a head scanning direction, although they perform heating corresponding to the type of print medium or pre-heating the print medium in a sheet conveyance direction. Further, Japanese Patent Application Laid-Open No. 63-317351 proposes moving a heating area in correspondence with movement of a printhead, thus saving heating energy. However, the heating area is moved in synchronization with the movement of the printhead and in dependence on the position information of the printhead. That is, none of these techniques aims to control permeation of the ink with respect to the print medium in accordance with image characteristics.
Accordingly, regarding feathering or bleeding, the above technique still has an unremovable problem. To obtain sharp character images in general documents, it is desirable that feathering or bleeding is prevented as much as possible. Characters can be clear if character portions and base portions, e.g., black portions and white base portions, are separated as clearly as possible. In so-called business color documents as well as black characters, the feathering or bleeding should be prevented as much as possible. In the business color documents, data in graphical representation such as a circle graph and a bar graph are formed by using various colors to visually assist people""s understanding of the documents. Further, in these documents, the base color is not always white but may be totally or partially another color. In these color documents, actual colors usually have a constant color hue and density in a specific region. Further, the number of colors is not so large. As mentioned above, if printed portions and base portions are clearly separated and feathering or bleeding is prevented as much as possible, high-quality color documents can be obtained, similar to character printing.
However, if a so-called natural image is printed by using this method, the following problem occurs. In a natural image, various colors are used. More specifically, at a very thin color portion, ink is often scattered in a wide area. To scatter ink in a wide area, various methods are employed. For example, if an area has constant color hue and intensity, dots are diffused in a regular pattern. Otherwise, an error diffusion method to diffuse dots by using prior and subsequent data can be used. However, in any method, a portion where high-density ink dots are scattered without spread is conspicuous to a human eye. In the above-mentioned business color documents, visual color data portions usually have uniform print patterns; therefore, the ink-scattered portions do not attract attention. However, in natural images, such portions are very unnatural, resulting in images which have excellent color representation but which have a rough-touch and poor quality.
To solve these problems, various methods are used; for example, ink which permeates into a print medium without causing spread, or a special print medium, is used. However, these methods are applied to the entire document sheet. That is, it is very difficult to print a document including a character portion which requires sharp edges, a color portion which requires vivid colors without color mixture, and a natural image portion which should avoid rough touch, on so-called normal paper, with high quality.
The present invention has been made to solve the above problems, and its object is to provide an ink-jet printer which print-outputs an image containing different types of images such as a natural image and a character image with high quality, and a printing method for the printer.
According to the present invention, the ink-jet printer to attain the foregoing object comprises: heating means for heating a desired area of a print medium; printing means for printing an image by discharging ink droplets onto the print medium; and control means for controlling said heating means and said printing means to heat an area of the print medium in accordance with control information while printing an image based on image information by discharging ink droplets onto the heated area.
Further, the printing method to attain the foregoing object comprises: a heat control step of heating an area, designated by control information, on a print medium; and a print control step of printing an image on the area heated at said heat control step.
By the above constructions, printing effects intended by a user can be attained by ink permeation control by totally or partially heating the surface of the paper.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.